Medical Weird eye viewing effect

That's my first post here, and I couldn't find any other place online where I can ask something like that and get rational scientific explanation. Here's what happened to me today and I have no idea what would cause it.

I went to a coffee shop in afternoon to take a break from work. While I was standing in line I started to look at the electronic LED display on cashier's machine where shows how much you need to pay. Out of nowhere I start feeling my heart beat and the numbers on the screen start looking like a drop hitting a still water with each heart beat. It happened 2 times in a row. Then I shook my head off, then I looked at it again, it happened one more time and it stopped. I don't have any weird sicknesses, mental illness, and I don't do any drugs. Just went through a cold about a week ago.

Honestly it does not make any sense to me, and it freaks the crap out of me. I hope it will never happen again, but still I'm trying to find any reasonable explanation to something like that.

It may have been an effect of eye movement. Despite what your brain makes you think, your eyes are never still; they jitter about constantly. Occasionally this can produce some strange effects, especially in conjunction with certain types of lights that have their own flicker.

Long and short of it: it's not uncommon. I would not fret about it, unless it starts recurring on a regular basis.